1. Field of the Invention
The present invention relates to a microwave lighting system and, more particularly, to a low-output microwave lighting system capable of enhancing a stability of a system by removing a flicker phenomenon generated at a low output and a flicker removing method using the same.
2. Description of the Background Art
Recently, a lighting system using microwave has been developed and is increasingly used thanks to its long life span and good luminance characteristics.
FIG. 1 is a schematic block diagram showing a construction of a conventional lighting system using microwave.
As shown in FIG. 1, a lighting system using microwave includes: a magnetron 10 generating microwave; a resonator 30 having an electrodeless bulb therein, resonating microwave supplied from the magnetron 10, and having a mesh form so that when the bulb converts microwave energy into light, the converted light can be discharged outwardly to its maximum; a wave guide 40 for guiding microwave generated from the magnetron 10 to the resonator 30; a high level voltage generator 50 for receiving power from an external source, boosting it to a high level voltage and supplying the high level voltage to the magnetron 10; a cooling unit 70 for cooling the magnetron 10 and the high level voltage generator 50 in order to prevent overheat of them due to a self-generated heat; a controller 60 for controlling the high level voltage generator 50 which applies the high level voltage to the magnetron and controlling an operation of the cooling unit 70; and a cooling completion memory unit 80 for memorizing whether cooling has been completed.
The operation of the conventional lighting system using microwave constructed as described above will now be explained.
First, the high level voltage generator 50 receives a drive signal outputted from the controller 60, increases AC power inputted from an external source, and supplies AC power of the increased high level voltage to the magnetron 10.
Thereafter, the magnetron 10 is oscillated by the high level voltage outputted from the high level voltage generator 50 and concentrates microwave with a very high frequency to the electrodeless bulb 20 in the resonator 30 through the wave guide 40. Accordingly, the electrodeless bulb 20 absorbs the microwave energy to generate light. At this time, when the high level voltage generator 50 is driven, the controller 60 drives the cooling unit 70 to cool the high level voltage generator 50, the magnetron 10 and the electrodeless bulb 20, in order to prevent the high level voltage generator 50 and the magnetron 10 from being overheated due to self-heating.
In order to actuate the lamp in an OFF state, the electrodeless bulb 20 should be sufficiently cooled for re-lighting the lamp. Thus, after the lamp is turned off, the cooling unit 70 is operated for a predetermined time to sufficiently cool the electrodeless bulb 20, a cooling completion state is recorded in the cooling completion memory unit 80, and then, the driving of the cooling unit 70 is stopped.
Thereafter, when the lamp is re-actuated, the controller 60 reads the content of the cooling completion memory unit 80, and if the cooling has been completed, the controller 60 re-actuates the lamp, or otherwise, the controller drives the cooling unit 70 for a predetermined time, and then, re-actuates the lamp.
The afore-mentioned microwave lighting system uses a linear high level voltage transformer in order to drive the magnetron.
FIG. 2 is a circuit diagram of the high level voltage generator using the linear high level voltage transformer in accordance with the conventional art, and FIG. 3 is an exemplary view showing an output waveform of the conventional microwave lighting system.
As shown in FIG. 2, in the conventional microwave lighting system, the electrodeless bulb is lighted by a secondary voltage generated by a voltage applied to a primary side of the linear high level voltage transformer. However, if the general AC power is increased to above a predetermined voltage, a power factor is degraded to increase a noise and a load of a circuit, resulting in degradation of stability of a system.
That is, as shown in FIG. 3, when a low-output lamp is lighted with a 120 Hz sinusoidal low-frequency input current in a state of plasma in a discharge tube, an instantaneous value of the lamp power is periodically changed, so that a temperature change in the discharge tube waves, generating a flicker phenomenon that a light source flickers. Then, a life span of the light system is shortened, a ripple is generated to cause an unstable lighting and degrade an efficiency of the lighting system. In addition, since the linear high level voltage transformer is large in volume and heavy in weight, a cost in construction of a facility (that is the lighting system) is increased.